Testing for interference with blood circulation is known, see the publication Prof. Volker, "Cardiac and Vascular Disorders" (English translation by Henry Mayer, M.D., published by Charles C. Thomas, second edition, Copyright 1965). The apparatus used is usually termed vasometric apparatus, to determine such interferences by vasography. A light sensor, which may be responsive to transmitted or reflected light is applied for example, to a toe of the person to be tested. The sensor is responsive to check the volume pulse of blood flow and provide representative electrical signals. The electrical signals, after amplification, are then displayed on a display monitor as a curve, or recorded on a curve drawing recording instrument. Curves are obtained from the right as well as the left side of the person to be tested, and upon comparison of the curves of similar digits, it is possible to determine the condition of blood vessels.
The measuring method described is subject to errors, in that the measuring result depends on the sensor as applied to the toe of the person to be tested, as well as on the maintenance of the foot in quiet and relaxed condition while the measuring takes place.
The digits to be tested may be the fingers or the toes of the person to be tested.